We have shortened purification of lens aldose reductase to two steps, an anion exchange column and an affinity column. This rapid, nearly quantitative procedure yields pure enzyme and has recently been adapted to small amounts of enzyme, i.e., from a single bovine lens or 3-4 pooled rat lenses. This allows us to obtain data on the pure enzyme obtained during the development of cataracts. Such studies are underway in rats on a high galactose diet and in streptozotocin induced diabetes in rats. We are currently recording by photography each stage of cataract, at the time the lenses are obtained for enzyme studies. One lens is used for determination of levels of oxidized and reduced coenzyme (NADPH/NADP+ ratios). The other lens is used to determine amount of enzyme and the kinetic constraints and properties of the pure enzyme from each stage of cataract development. Other researchers have focused on sugar alcohol accumulation and cataract formation in lens primarily as a function of blood sugar levels. Research was directed mainly at the control by close regulation of blood sugars and administration of inhibitors of aldose reductase. Extensive efforts have not been directed toward determination of the quantity and characteristics of the enzyme despite the distinct possibility that kinetic alterations of the enzyme protein may be a primary cause of sugar alcohol accumulation and cataracts. Since aldose reductase is the initial step in the sorbitol pathway, it is likely that regulation of this enzyme is a critical determinant in sugar alcohol production.